In some applications, such as automotive vehicle manufacturing, it is common to have multiple heat exchangers for cooling or heating various different fluids that are used in the application. For example, in the case of an automobile, it is common to have a radiator for cooling the engine coolant, and one or more other heat exchangers for cooling such fluids as engine oil, transmission oil or fluid, power steering fluid, etc. Usually, air is used to cool the engine coolant, and often the engine coolant itself is used to cool the other fluids, such as engine or transmission oil or power steering fluid. As may be appreciated, this usually involves a lot of plumbing, and in automotive applications, it is highly undesirable to have too many components that need to be assembled into the automobile, as that increases the cost of assembly, provides more components that can break down, and it takes up valuable space, which is always in short supply.
In an attempt to reduce the amount of plumbing required and to save space, it has been proposed to combine two heat exchanger functions or heat exchanger subassemblies into a combination heat exchanger, where one of the fluids, such as engine coolant is shared between the two subassembly heat exchangers. An example of this is shown in U.S. Pat. No. 4,327,802 issued to Beldam, where the same engine coolant used in the radiator is used in an oil cooler subassembly formed integrally with the radiator. In this Beldam heat exchanger, air is used to cool engine coolant and in turn, the engine coolant is used to cool oil.
U.S. Pat. No. 5,884,696 (Loup) is another combination heat exchanger, where interleaved fluid flow passages are used to put two heat exchangers in parallel and reduce the overall size of what would otherwise be too separate heat exchangers. In this device, adjacent flow passages for the two heat exchange fluids, such as engine coolant and refrigerant, are separated by air passages for heat transfer between the two heat exchange fluids and the air.
Yet another example of a combination heat exchanger where heat energy is transferred between a common fluid and two other fluids is shown in U.S. Pat. No. 5,462,113. In this device, two refrigerant circuits with alternating spaced-apart flow passages are provided, and a third heat exchange fluid, such as water, surrounds all of the refrigerant circuit flow passages, so that maximum exposure of the water to the refrigerant is achieved.
While all of the above-mentioned prior art devices achieve the desired result of compact design and simplification of the plumbing, they are all concerned with transferring heat between one common fluid and two other fluids. They are not concerned with transferring heat energy between the two other fluids per se, and consequently, they are not very efficient at doing that.